U.S. Pat. No. 5,601,307 discloses a vehicle suspension system in which a double-acting hydraulic ram supports the vehicle at each wheel with the ram chambers at opposite diagonal comers of the vehicle cross-connected so as to provide four discrete hydraulic wheel circuits. A load distribution unit is connected to the four hydraulic circuits for hydraulically equalizing the pressures in the circuits. FIG. 5 of U.S. Pat. No. 5,601,307 discloses a load distribution unit (LDU) 140 which includes a pair of cylinders, each containing a double-acting ram that divides the cylinder which contains it into four variable volume chambers, one chamber at each end of the ram and two chambers inward of the two end chambers, each chamber being isolated from all the others. Each of the inward chambers communicates with a different one of the wheel circuits, with each LDU cylinder being connected to the same chambers of the wheel cylinders on opposite sides of the vehicle, i.e. one of the inward chambers of one of the LDU cylinders is connected to the wheel cylinder circuit that connects the front left upper wheel cylinder with the rear right lower wheel cylinder, and the other inward chamber of the same LDU cylinder is connected to the wheel circuit that connects the front right upper wheel cylinder with the rear left lower wheel cylinder. In the same manner, the other LDU cylinder is connected to the two wheel circuits that connect the front lower wheel cylinders with the rear upper wheel cylinders. A total of six (one for each of the four inward chambers, plus one for each of the two end chambers of different LDU cylinders that are connected) solenoid-operated pressure supply valves 204 are supplied for providing hydraulic fluid under pressure to the various chambers of the LDU, and a total of six pressure relief or drain valves 215 are provided for relieving pressure from the various chambers. In addition, a reservoir 66 is provided for the hydraulic fluid, together with a pump 65 and gas-charged accumulators 202 for maintaining pressure in the system.
Such a vehicle suspension system requires several solenoid operated hydraulic valves. The coils must be small, highly reliable, pull-in with relatively high forces at vehicle voltages (typically 12 VDC), and maintain actuation with high dynamic forces, exerted not only by the fluid, but also by the movement of the vehicle. The present invention provides a valve coil pack which contributes to the solution of these problems.